A prime mover of a hybrid vehicle is comprised of a plurality of different kinds of power units such as an engine adapted to generate a power by converting a thermal energy into a kinetic energy, and a motor having a generating function. In the hybrid vehicle, therefore, an energy efficiency can be optimized and an exhaust gas can be reduced by taking advantages of the engine and the motor. One example of the hybrid vehicle of this kind is described in Japanese Patent Laid-Open No. 2011-213147 (US2011/0245003).
In the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147, a prime mover is comprised of an engine, and a first and a second motors. According to the teachings of Japanese Patent Laid-Open No. 2011-213147, the hybrid drive device is comprised of an input shaft connected with the engine, an output shaft connected with driving wheels, and a power distribution device as a single pinion type planetary gear unit. Specifically, the power distribution device is comprised of a ring gear connected with the output shaft to serve as an output element, a carrier connected with the input shaft to serve as a distribution rotary input element, and a sun gear connected with the first motor to serve as a reaction element. The hybrid drive device is further comprised of a speed change mechanism including four rotary elements such as a speed change input rotary element, a first output rotary element, a second output rotary element, and a fixed rotary element. Specifically, the speed change mechanism is comprised of: a Ravigneaux planetary gear unit having a first sun gear serving as a fixed rotary element, a common ring gear serving as a first output rotary element, a common carrier serving as a second output rotary element, and a second sun gear serving as a speed change input rotary element; and a single pinion type planetary gear unit having a ring gear, a carrier, and a sun gear. In addition, the hybrid drive device is further comprised of: a first engagement device that selectively fixes the second sun gear of the Ravigneaux planetary gear unit; a second engagement device that selectively fixes the ring gear of the single pinion type planetary gear unit; and a third engagement device that selectively fixes the common ring gear of the Ravigneaux planetary gear unit.
The hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147 is adapted to select an operation mode from a first split mode, a second split mode, and a third split mode. Specifically, the first split mode is selected in the middle speed range of the three split modes by engaging the first engagement device while disengaging the second and the third engagement devices. The second split mode is selected in the highest speed range of the three split modes by engaging the second engagement device while disengaging the first and the third engagement devices. The third split mode is selected in the lowest speed range of the three split modes by engaging the third engagement device while disengaging the first and the second engagement devices.
Japanese Patent Laid-Open No. 2008-120139 also describes a hybrid drive system in which a prime mover is comprised of an engine, a first motor, and a second motor. The hybrid drive system taught by Japanese Patent Laid-Open No. 2008-120139 is comprised of planetary gear unit serving as a power distribution device to perform a differential action among three rotary elements such as a sun gear connected with the first motor, a ring gear connected with an output shaft, and a carrier connected with the engine. The hybrid drive system is further comprised of a speed change mechanism adapted to select a speed ratio from two ratios. Specifically, the speed change mechanism is comprised of a stepped pinion type planetary gear unit having a diametrically large first sun gear and a diametrically small second sun gear, and two brake devices. The second motor is connected with an output side of the speed change mechanism, and an output shaft is connected with an output side of the speed change mechanism. In addition, the hybrid drive system is further comprised of a clutch device adapted to selectively connect the carrier of the power distribution device and the second motor thereby selectively connecting the engine with the second motor.
In the hybrid drive system taught by Japanese Patent Laid-Open No. 2008-120139, an operating mode can be selected from an output split mode and a directly-connected mechanical deceleration mode. Specifically, the output split mode is established by bringing the speed change mechanism into a neutral state while engaging the clutch device to connect the engine with the second motor. Meanwhile, the directly-connected mechanical deceleration mode is established by allowing the speed change mechanism to transmit a torque while engaging the clutch device to connect the engine with the second motor.
Thus, in the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147, the drive mode is selected from the first split mode, the second split mode, and the third split mode depending on a vehicle speed and a required drive force. According to the teachings of Japanese Patent Laid-Open No. 2011-213147, the drive mode is shifted while synchronizing rotational speeds of the first output rotary element and the second output rotary element of the speed change mechanism individually with rotational speeds of the output rotary element and the distribution rotary input element of the power distribution device. Therefore, the speed change mechanism is not necessarily to be brought into the neutral state so that shocks and a torque drop can be reduced.
As described, in the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147, the power distribution device and the speed change mechanism are comprised of three planetary gear units and three engagement devices, and a structure of the Ravigneaux planetary gear unit is rather complicated. Therefore, it is not easy to downsize the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147 having such a complicated structure. As also described, in the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147, the drive mode is selected from three modes depending on a vehicle speed. However, the hybrid vehicle is expected to be driven in various situations. For example, the hybrid vehicle may be driven under the situation where a state of charge (abbreviated as SOC hereinafter) is low. In contrast, the hybrid vehicle may be powered only by the motor. Otherwise, there may be a case where a large drive force is required when the hybrid vehicle runs backwardly. That is, it is difficult to cover all of those situations only by the drive mode selectable in the hybrid drive device taught by Japanese Patent Laid-Open No. 2011-213147.
Thus, the conventional hybrid drive units are required to be modified to increase available drive modes to cover various running conditions while being downsized and structurally simplified.
The present invention is conceived noting the foregoing technical problems, and an objective of the present invention is to provide a hybrid drive unit to realize a variety of drive modes for covering various running conditions.